A secondary battery is a chargeable and rechargeable battery employing a fine electrode material, where a representative example of commercialization thereof is a lithium secondary battery. The lithium secondary battery is expected to be applied as a small power source for a small IT device, such as a smart phone, a portable computer, and an electronic paper, but also as a mid-sized or large-sized power source mounted on a means of transportation, such as a car, or used in a power storage in a power supply network, such as a smart grid.
If lithium metal is used as an anode electrode material of a lithium secondary battery, the battery may be short-circuited or explode due to formation of dendrite. Therefore, a crystalline carbon, such as graphite or artificial graphite, soft carbon, hard carbon, or a carbon-based active material capable of intercalating and deintercalating lithium is commonly used instead of the lithium metal for an anode electrode. However, as fields of application of a secondary battery expand, it is demanded to further increase capacity and output power of a secondary battery, and thus non-carbon-based anode electrode materials that have capacities of 500 mAh/g or higher and may be alloyed with lithium, such as silicon (Si), tin (Sn), or aluminum (Al), are being spotlighted as materials for replacing carbon-based anode electrode materials having a theoretical capacity of 372 mAh/g.
From among the non-carbon-based anode electrode materials, silicon exhibits the largest theoretical capacity of about 4,200 mAh/g, and thus utilization of silicon is very important in terms of capacity. However, volume of charged silicon is about 4 times greater than that of discharged silicon. Therefore, due to change of volume during charging and discharging operations, electric connection between active materials is destroyed, an active material is detached from a current collector, and an irreversible reaction deteriorating life expectancy of a battery, such as formation of a solid electrolyte interface (SEI) layer like a Li2O layer due to corrosion of the active material due to an electrolyte, occurs, and thus it is difficult to utilize silicon as a anode electrode material.
To overcome the problems, a method of fabricating a nano-size active material, a method of enhancing surfaces of an active material by using graphene or carbon, and a method of synthesizing materials having various structures have been suggested. Furthermore, a technique for resolving problems of a anode electrode based on charging/discharging operations by forming a plurality of grooves with semicircular cross sections or a plurality of hemispherical grooves by wet-etching a surface of a current collector foil or forming nano-wires grown to have first ends substantially fixed to a current collector foil on an upper portion of the current collector foil and depositing an active material thereto via a physical vapor deposition has been suggested. However, in this case, since an active material layer covering all of the nano-wires is formed, and thus the active material may be exfoliated and it is difficult to effectively increase a ratio of specific surface area to volume due to the nano-wires.